Does anyone know how I can lose 15 lbs?

So, I am 12 almost 13 and have been trying to lose weight for a while, And finally just be lean. I'm not a crazy anorexic or anything but I was really upset today because i run with my dad about 3 miles 3x a week and this week i decided to run everyday to lose weight. I am currently as of my recent weigh-in 109.0 lbs.): I've been trying to reach 94.0lbs because in the summer i weighed 97-99 lbs and i STILL had chub on my stomach. My legs and arms are pretty thin but my stomach is big. You can't tell when i'm wearing clothes, but it is. I have four big roles on it and just trust me- It is. My dad even sais he thinks i should lose no more than 15 lbs!!! And i freaked out because thats alot. So tuesday i ran 2 miles and did situps everyday this week, Wednesday i ran 2 miles Thursday i ran 2 miles friday i ran 3 miles and saturday i walked, jogged and played sports and sunday i ran 3 1/2 miles and i hadn't eaten anything yet and weighed myself..And guess what? I'd only lost 3 Lbs! I know it's better than nothing, but i was still upset because just think if i wouldve only ran 3 times that week, i'd probably only would've lost 1 pound! AND BELIEVE ME I WORKED SO HARD THAT WEEK AND EACH DAY I ONLY ATE 3 HEALTHY MEALS WITH NO SNACKS! I just don't know what to do anymore and don't know how to reach my goal! Also today after i weighed myself i ate fettucini alfredo at beppo unos and had icecream afterwards and then i came home and couldn't resist...i weighed myself and weighed 109.0lbs! I'd gained it all back! so that whole week was pointless!!! I really need a plan that will work. I'm starting cross country soon but don't even know if that will get me to lose the weight. Please help[!!! I really wanted to weigh about 100lbs for the last day of school which is 12 days away...I was really excited to weigh that but it looks like i'm not going to..That'd be 9 lbs in 12 days...So leave your answers and tell me how i can get rid of my fifteen pounds or atleast how to lose nine pounds in twelve days!